Windows Cursor Resource (.cur)
Microsoft StandardWindows Cursor Resource (CUR) is the native Microsoft Windows mouse pointer format, identical in container architecture to ICO but specifying exact hotspot coordinate offsets.
Inspect & Metadata
Operating systems and file analyzers identify CUR files by inspecting the leading binary byte sequence:
Byte-Level Header Signature (Magic Bytes)
Operating systems and file analyzers identify CUR files by inspecting the leading binary byte sequence:
HEX SIGNATURE (OFFSET 0):
00 00 02 00ASCII REPRESENTATION: ....
Standardization: Microsoft Windows Resource Specification
Technical Specifications
| Container Architecture | ICONDIR header with resource type 2 (Cursor) followed by ICONDIRENTRY array and DIB data |
| Compression | Uncompressed DIB or PNG compressed streams (Windows Vista+) |
| Byte Endianness | Little-Endian (Intel x86) |
| Color Spaces | Device RGB |
| Channels & Structure | 1-bit monochrome mask, 4-bit, 8-bit, or 32-bit BGRA with alpha |
| Max Dimensions | Typically 32 x 32, 48 x 48, or 64 x 64 (supports up to 256 x 256 in modern Windows) |
| Transparency | XOR/AND binary mask or 8-bit smooth alpha channel |
| Streaming & Progressive | Non-streamable desktop icon/cursor directory |
Technical Comparison Matrix: CUR vs Competitors
| Technical Attribute | CUR (Current) | ICO | PNG | SVG |
|---|---|---|---|---|
| Hotspot Definition | Embedded X/Y pixel coordinates | None (center/top-left default) | Defined in CSS | Defined in SVG viewbox |
| Resource Type ID | 0x0002 (Cursor) | 0x0001 (Icon) | Standard image | Vector XML |
| Operating System | Native Windows Mouse Subsystem | Windows Shell / Browser Favicon | Universal Web & App | Universal Vector |
| Scalability | Fixed multi-resolution mipmaps | Fixed multi-resolution mipmaps | Raster fixed size | Infinite vector scaling |
Common Corruption Modes & Hex Recovery Guide
Mouse click registers several pixels away from the tip of the cursor arrow.
Root Cause: Corrupted or missing Hotspot X/Y coordinates in the ICONDIRENTRY table.
Recovery: Re-author cursor in File2File Cursor Converter to visually recalibrate the hotspot coordinate.
Security Analysis & Parser Attack Vectors
CUR parsing bugs in the Windows Graphics Device Interface (GDI) historically allowed arbitrary code execution via crafted header dimensions.
Known Attack Vectors
- Integer overflow during allocation of DIB color masks in legacy cursor decoders.
- Corrupted hotspot offsets triggering out-of-bounds pointer reads during cursor blitting.
- Heap corruption when parsing embedded PNG streams within modern CUR files.
Defensive Best Practices: Validate hotspot coordinates are strictly within frame dimensions (0 <= X < Width, 0 <= Y < Height).
Historical Origins & Milestones
Key Advantages & Pros
- Defines exact pixel hotspot coordinates (X, Y) where mouse clicks physically register on screen.
- Enables multi-resolution cursor definitions for sharp display on standard and high-DPI 4K monitors.
- Direct native operating system support in Windows without third-party pointer drivers.
Technical Limitations & Cons
- Windows-centric format with poor native display support on mobile devices and non-Windows browsers.
- Static pointer only; animated cursors require the multi-frame .ANI container.
- Legacy 1-bit XOR masks produce harsh inversion artifacts on modern color interfaces.
Interesting Technical Trivia
- The only structural difference between an ICO file and a CUR file is byte 3 of the header: 1 for Icon, 2 for Cursor.
- In an ICO file, bytes 4 and 6 of each entry represent color planes and bits per pixel; in a CUR file, those exact bytes represent the Hotspot X and Y coordinates.
- CSS supports custom web cursors directly using URLs pointing to .cur files.
Frequently Asked Technical Questions
What is a cursor hotspot?
A hotspot is the exact pixel coordinate inside the cursor image (such as the very tip of an arrow or the center of a crosshair) where click events occur.
Can I convert an image (PNG/JPG) to a CUR file?
Yes. File2File.app allows you to convert standard PNG or JPG files into Windows .CUR cursor files with custom hotspot placement.
How can I use a .cur file on my website?
You can apply custom cursors in CSS using: cursor: url('my-cursor.cur'), auto;